Apparatus for controlling or assisting respiration



Jan. 5, 1965 5. A. WHITE ETAL 3,164,149

APPARATUS FOR CONTROLLING 0R ASSISTING RESPIRATION Filed Feb. 3. 1961 United States Patent 3,164,149 APPARATUS FOR CONTROLLING 0R ASSETING RESPIRATKQN Gerald Alfred White, Brooirhouse, near Lancaster, and Ian George Baxter, Harlow, England, assignors to The British Oxygen Qompany Limited, a British company Filed Feb. 3, 1961, Ser. No. 36,903 Claims priority, appiication Great Britain, Feb. 3, 1%0, 3,823/60 4 Claims. (Cl. 128-29) This invention relates to automatic ventilators for producing controlled or assisted respiration. Such ventilators are used for example on those having respiratory paralysis or disability, for resuscitation, prolonged artificial respiration or during anaesthesia.

In a particular type of automatic ventilator commonly termed pressure cycled, air or some other mixture of gases containing oxygen is delivered to the patient from a source under pressure through a valve means, until a certain level of positive pressure is attained in the supply line to the patient. At this prescribed pressure, the valve means is operated so as to shut off the supply of gas mixture, and permit free exhalation by elastic recoil of the lungs. Provision may be made for expiration to be assisted by the application of suction which may, if desired, be sufiicient to produce a negative pressure in the lungs. At the end of the exhalation phase, the duration of which may be time controlled or may be terminated by the production of a predetermined minimum pressure in the lungs, and preferably after an interval of time corresponding to the respiratory pause of natural breathing, the valve means is operated to restore the flow of gas mixture so as to initiate the next inspiration phase. This cycle is repeated for as long as may be necessary. Always included as an essential part of the mechanism of a pressure-cycled ventilator is a pressure-sensing element responsive to a pressure closely related to the pressure in the patients lungs.

In an alternative type of automatic ventilator termed volume-cycled, the patients lungs are filled with a measured volume of gas mixture at each breath, instead of being inflated to a predetermined pressure.

It is accepted practice to convert a fundamentally pressure-cycled automatic ventilator into a volume-cycled one by the addition of a secondary gas circuit, comprising a rigid chamber containing an expansible bag or bellows that is interposed at some point in the tubing between the valve means and the patient, the interior of the bag being in communication with the patients lungs, whilst the space outside the bag is in communication with the outlet from the valve means. If the apparatus is to be used in open circuit, a non-return valve is placed in the secondary gas circuit between the bag and the patient to prevent rebreathing. For closed circuit operation a C0 absorber is interposed. If some arrangement is provided for limiting the volumetric excursion of the bag, and the pressurecycling mechanism is adjusted to trip the valve at a higher pressure level than will occur under normal conditions, then volume-cycling operation will be obtained, because each inspiratory phase will be limited in duration by the swept volume of the bag.

It is an object of the present invention to provide an improved volume-cycled ventilator, based on a volume metering principle that eliminates the unwieldy secondary gas circuit.

According to the present invention an automatic ventilator comprises primary valve means adapted to control the flow of gas admitted thereto from a source of gas under pressure, a pressure responsive member coupled to the valve means and movable in response to a predetermined change in the pressure applied thereto to close the valve "ice means and automatically movable after a predetermined interval to open the valve means, and a flowmeter located in the path of the gas flow downstream of the valve means, said flowmeter being adapted in response to the flow of a predetermined volume of gas to move the pressure responsive member to close the valve means.

The flowmeter may be arranged to open secondary valve means for admitting fiuid under pressure from a subsidiary source to the pressure responsive member whereby it moves to close the primary valve means. Provision is made for resetting the flowmeter so as to close the secondary valve means as soon as the primary valve means is closed.

According to a feature of the invention the means for resetting the flowmeter is associated with and operated substantially simultaneously with the primary valve means.

The pressure responsive member may be a flexible bellows adapted to be inflated by the subsidiary source of fluid under pressure, and provided with an adjustable bleed to atmosphere, the interval of time during which the flow of gas is cut off being determined by size of the bleed.

The flowmeter may consist of a windmill, turbine, or displacement pump type of instrument, coupled to some form of counter or integrating device.

In a preferred form of the invention the flowmeter comprises a linear flow resistance element, the pressure drop across the element being transformed linearly into a measurable variable such as volume, pressure, or electrical voltage, which is integrated with respect to time to obtain an output signal proportional to the volume of gas passing the valve means. When this signal reaches a predetermined magnitude corresponding to the volume of gas it is desired to supply at each inspiration, it is adapted to open the secondary valve means whereby fluid under pressure is applied to the pressure responsive member. The term linear flow resistance element in this instance connotes a porous partition, a honeycombed duct, a wad of fibrous or spongy material, or any other element in which the relationship between the rate of gas flow therethrough and the pressure drop across it is linear.

An automatic ventilator constructed in accordance with the invention will now be described by way of example with reference to the accompanying drawing in which it is shown in diagrammatic section.

A supply of gas, for example oxygen is delivered under pressure through a passage 1 to a chamber 2 having an outlet 3 communicating with an injector 4 through which gas is discharged into a passage 5 connected to the patients supply line. Passage of gas through the injector is arranged to entrain at 6 either air or anaesthetic gas according to the patients requirements. Valve means for controlling the flow of gas to the injector 4 consists of an elongated valve member 7 which is arranged to pivot at its mid-point about a pin 8 and is adapted at one end to close the outlet 3. The valve member 7 is magnetically coupled to a flexible bellows 9 by means of a fixed magnet 16 and a movable magnet 11, the latter being carried by the bellows. This magnetic coupling imparts a snap action to the valve and prevents premature opening thereof. The bellows is provided with a vent pasage 12 controlled by a fine adjustment valve 13 and is loaded by means of a compression spring 14 acting through a pivotally mounted lever 15.

A flowmeter for controlling the volume of gas delivered at each operation of the valve consists of a linear flow resistance element 16 located in the passage 5 through which gas mixture is delivered to the patient. Leading from the passage 5 on the upstream and downstream sides respectively of the resistance element 16 are pass-ages 17 and 18 which open into sides 19 and 20 respectively of a volume control chamber divided into two by a yielding V v 3 v partition 21. A second linear flow resistance element 22 is located in the passage 17. The element 22 is shown as an adjustable bleed whereby the resistance to flow is variable but for some purposes a local narrowing of the lumen of the passage may sufiice. Secured to the yielding partition 21 is a plunger 23 which is adapted to be moved by the partition to open a secondary valve means 24 controlling the fiow of gas through a passage 25, which leads from the main supply line l, to a passage 26 which leads into the bellows V The side 1? of the volume control chamber is provided with a spring loaded pressure relief valve 27 adapted to be opened by a jet of gas under pressure delivered through a passage 2?, the inlet end 29 of which is located in the chamber 2. The inlet 29 co-operates with the valve member 7.

In operation, at the beginning of the inhalation phase when the bellows 9 is deflated, that end of the valve member 7 which co-operates with the outlet 3 is attracted by the magnet 11 so that the primary valve means is open.

Oxygen under pressure then flows from the chamber 2 to the injector 4 and thence through the linear flow resistance element 1'5 in the passage 5 to the patient. A proportionate drop in pressure is established across the resistance element which in turn causes a subsidiary flow of gas through the variable linear flow resistance element 22 so as to displace the yielding partition 21. Since the partition has a substantially constant efiective area it moves at a velocity proportional to the primary flow rate in passage 5, and correspondingly, the distance through which the partition is displaced during a given interval of time is proportional to the volume of gas delivered through the passage 5 during that period. On displacement of the partition 21 through a preset distance, the plunger 23 is caused to open the secondary valve means 24 whereby gas is admitted to the bellows 9. As the bellows expands, the attraction between the magnet 11 and the end of the valve member 7 co-operating with the outlet 3 decreases until it is overcome by the attraction between the fixed magnet in and the other end of the valve member. The valve member then pivots about the pin g to close the outlet 3, thus terminating the inhalation phase. The duration of the exhalation phase is determined by the time taken for the bellows 9 to collapse which in turn is controlled by the fine adjustment valve 13.

At the end of each inhalation phase when the valve member 7 moves'to close the outlet 3 it automatically opens the inlet 29 thus permitting oxygen under pressure to flow through the pasage 28 and cause the pressure relief valve 27 to open. The jet of oxygen discharges through the valve 27, at the same time functioning as an ejector device to suck gas from the side H of the volume control chamber whereby the partition 21 is permitted to return to its initial position preparatory to the beginning of the next inhalation phase.

We claim:

1. An automatic ventilator comprising a source of fluid under pressure, means defining a primary chamber, an inlet for conducting fluid under pressure from said source into said primary chamber, an outlet for conducting fluid under pressure out of said primary chamber magnetically responsive primary valve means movable between open reams and closed positions to control the discharge of fluid under pressure from said primary chamber through said outlet in accordance with variations in a pressure condition, a pressure responsive member magnetically coupled to said primary valve means movable in responses to a predetermined increase in said pressure condition to magnetically actuate said primary valve means from said open to said closed position, said pressure responsive means automatically movable upon a predetermined decrease in pressure to magnetically actuate said primary valve means back to said open position to discharge fluid under pressure from said chamber, conduit means connected to said outlet in said chamber for conducting said discharged fluid away from said chamber, and a flow meter downstream of said primary vale means connected to the conduit means and in the path of said discharged fluid under pressure, said flow meter including means for selectively connecting and disconnecting said source of fluid under pressure to said pressure responsive member.

2. An automatic ventilator according to claim 1 wherein said how meter includes a how resistance element disposed in said conduit means downstream of said primary valve, a volume control housing, pressure sensing means dividing said volume control housing into first and second chamber portions, means defining first and second passages, said first passage connected to said first chamber portion and said conduit upstream of said flow resistance element, said second passage means connected to said second chamber portion and said conduit downstream of said flow resistance element, said sensing means movable from an initial position to an actuating position in response to variations in pressure conditions in said first and second chamber portions, and actuating means connected to said sensing means for selectively connecting and disconnecting said source of fluid under pressure to said pressure responsive member in accordance with the predetermined variations in pressure conditions in said first and second chamber portions.

3. An automatic ventilator according to claim 2 wherein said first chamber portion in said volume control housing is selectively connected to the interior of said primary chamber in accordance with a pressure condition, said primary valve means in said primary chamber adapted to prevent communication between said primary chamber and said first chamber portion when said primary valve is in the open position with respect to said outlet.

4. The automatic ventilator according to claim 3 wherein said first chamber portion includes pressure relief means movable between open and closed positions, said means normally closed, said means moved to said open position when said primary valve moves to said closed position.

References fitted by the Examiner UNITED STATES PATENTS 2,915,056 12/59 Lee l2829 2,969,789 1/61 Morch 128-29 3,088,455 5/63 Black 128-29 LOUIS R. PRINCE, Primary Examiner.

ADELE M. EAGER, Examiner. 

1. AN AUTOMATIC VENTILATOR COMPRISING A SOURCE OF FLUID UNDER PRESSURE, MEANS DEFINING A PRIMARY CHAMBER, AN INLET FOR CONDUCTING FLUID UNDER PRESSURE FROM SAID SOURCE INTO SAID PRIMARY CHAMBER, AN OUTLET FOR CONDUCTING FLUID UNDER PRESSURE OUT OF SAID PRIMARY CHAMBER MAGNETICALLY RESPONSIVE PRIMARY VALVE MEANS MOVABLE BETWEEN OPEN AND CLOSED POSITIONS TO CONTROL THE DISCHARGE OF FLUID UNDER PRESSURE FROM SAID PRIMARY CHAMBER THROUGH SAID OUTLET IN ACCORDANCE WITH VARIATIONS IN A PRESSURE CONDITION, A PRESSURE RESPONSIVE MEMBER MAGNETICALLY COUPLED TO SAID PRIMARY VALVE MEANS MOVABLE IN REPSONSES TO A PREDETERMINED INCREASES IN SAID PRESSURE CONDITION TO MAGNETICALLY ACTUATE SAID PRIMARY VALVE MEANS FROM SAID OPEN TO SAID CLOSED POSITION, SAID PRESSURE RESPONSIVE MEANS AUTOMATICALLY MOVABLE UPON A PREDETERMINED DECREASE IN PRESSURE TO MAGNETICALLY ACTUATE SAID PRIMARY VALVE MEANS BACK TO SAID OPEN POSITION TO DISCHARGE FLUID UNDER PRES- 